v3.9.0

Added

• show metadata.json version preview in release.sh begore confirmation

Changed

• move metadata.json version bump from changelog.sh to release.sh
• fix metadata version to current on GNOME Extensions
• add donations field to metadata.json with Buy Me a Coffee link
• add Buy Me a Coffee support section to README
• add FUNDING.yml with Buy Me a Coffee link
• document when not to create a release in RELEASING.md
• add warning emoji to version lag notice in README
• move version lag note to blockquote in README